In general I have found that after a few months service most fans give materially less than the maker's rating and allowance should be made for this in buying a fan.
Steam-jet Blowers.—Steam jets have long been used for "blowing" or exhausting in order to maintain combustion in locomotive boilers, usually employing the exhaust from the engines through properly shaped " nozzles/' This type of air compressor or exhauster also finds extended application for emergency use and at times in permanent installations for removing foul air from mines, factories, ship holds, and for gas exhausters, for securing forced draft, and for handling gases under low pressures in certain chemical industries. Among its advantages are simplicity, ease of operation, small space, minimum of repairs and ease of regulation.
A. von Ihering ("Die Geblase") reports some tests as to steam consumption which indicate from 1.3 to 3.4 Ib. of steam required per 1,000 cu. ft. of air handled, the larger sizes being the more economical.
Hydraulic Compressors.—Several devices have been made for utilizing falling water for the purpose of compressing air without the use of any mechanical moving parts. The most successful of these is the Taylor compressor, shown dia-grammatically in Fig. 24. In the figure, air tubes are represented at C, all terminating at the conical entrance B to the down-flow pipe E. The water supply is furnished through the flume D. As the water falls it draws air through the small tubes, carrying it down to the separating tank(j, where it is liberated at a pressure depending on the weight of water in the vertical pipe H. The compressed air is then conducted through the pipe K to the place where it is to be used. The distance from M to the tail race L represents the height or fall of water that is available.
In this system the compression is isothermal and the compressed air is saturated with moisture. The oxygen content of the air is reduced, which renders the air less beneficial for purposes of mine ventilation if the exhaust from the air tools is planned to assist ventilation. The system offers
FIG. 24.—Taylor hydraulic air compressor.
Air measurements, absolute pressures
Free air, cubic feet per minute Free air, pounds per square inch Compressed air, pounds per square inch Horsepower Cubic feet per minute Head, feet Horsepower Efficiency, per cent
10,580 14 128 1,430 13,057 70.5 1,741 82.17
11,930 14 128 1,623 14,820 70.0 1,961 82,27
9,238 14 128 1,248 12,710 70.6 1,700 73.50
a very simple solution for utilizing water powers when the market for compressed air justified its installation. It has the advantage of simplicity with a minimum of operating expense, and very high efficiencies are secured. The first cost of the installation is likely to be high.
Figure 25 illustrates some of the dimensions of a Taylor hydraulic compressor installed near Cobalt, Ontario, Canada. This was designed for a capacity of 40,000 cu. ft. of free air per minute to be compressed to a gage pressuae of 120 Ib. The compressed air is conducted to mines through 9 miles of 20-in. pipe leading to two 12-in. lines with a total distributing line of 21 miles in length. The water is admitted